The present invention relates to a technique for depositing a platinum film, which is used as a bottom electrode for capacitors of dynamic random access memory (DRAM) cells or of non-volatile memory cells and film sensors. More particularly, the invention relates to a technique for controlling the preferred orientation of the platinum films by depositing the platinum under an atmosphere containing nitrogen as well as an inert gas and then annealing to remove the nitrogen which was introduced during the deposition of the platinum. The present invention also relates to a method of manufacturing semiconductor devices or sensor devices comprising such platinum thin films.
In order to increase the capacitance of a DRAM cell capacitor to meet the requirements of increasingly high integration of semiconductor memory devices, several approaches (e.g., (i) decreasing the thickness of dielectric material films, (ii) increasing the effective area of the capacitor, and (iii) using materials with high dielectric constant as dielectric oxide films) have been proposed. However, decreasing the thickness of a dielectric material film to less than 100 .ANG. deteriorates reliability of the semiconductor device due to the Fowler-Nordheim current. Increasing the effective area is complicated in its process and incurs high manufacturing cost. Moreover, deposited layers are not uniform and leakage current is generated between the trenches when applied to a laminate-type capacitor and a trench type capacitor, respectively. Thus, these two conventional methods have limitations especially when applied to high density memory cells of higher than 1 Gbit. The third proposed method to use high-ielectric materials is currently being investigated to form capacitors of DRAM cells, which have conventionally used polysilicon as the bottom electrode material. However, such high-dielectric oxide films need to be formed under an oxidation atmosphere and high temperature (higher than 500.degree. C.), which may result in problems relating to the polysilicon. For example, if polysilicon is employed as the bottom electrode in using high-dielectric materials as a capacitors, serious problems may occur due to oxidation of the polysilicon under the high temperature (over 500.degree. C.) and oxidation atmosphere during formation of the highdielectric oxide thin films. For this reason, platinum is being investigated for use in place of polysilicon as an electrode of a DRAM cell employing a high-dielectric oxide, because platinum is stable under high temperature and oxidation atmosphere.
Moreover, it is well known that the properties of anisotropic crystals depend on their crystallographic orientations. The crystallographic orientations of oxide films formed on bottom electrodes depend on the crystallographic orientation of the bottom electrodes. Therefore, it is believed that controlling the preferred orientation of bottom electrodes is very important in controlling the preferred orientation of oxide fils in order to have films with desirable physical properties.
High-dielectric/ferroelectric materials are used for not only DRAM cells but also other electronic devices such as non-volatile ferroelectric memory devices, ferroelectric sensors or actuator devices, etc. Platinum is most favored, in particular, as a bottom electrode of such high-dielectric/ferroelectric devices. The favored high-dielectric and ferroelectric materials are oxides having perovskite structure, bismuth-layered perovskite structure and tungsten-bronze type structure along with ReMnO.sub.3 (Re: rare earth element) and BaMF.sub.4 (M: Mn, Co, Ni, Mg, Zn).
It is known that a platinum thin film, which is deposited on an insulating oxide layer by the conventional method, generally has a preferred (111) orientation. This is due to the fact that the plane with the minimum surface energy in metals with face centered cubic (FCC) structure is (111) and, considering only the surface energy at the depositing, the film is most stable if oriented toward (111).
Conventional methods for forming preferred orientation-controlled platinum films which have been suggested have limitations. In order to change the preferred orientation of the platinum film, one such conventional method that has been suggested is forming the platinum film on a single crystal substrate of the materials such as MgO, NaCl, KBr, SrTiO.sub.3, LaAlO3. However, such a method not only is complicated in its process and incurs high unit costs for single-crystalline substrates but also is incompatible with the state-of-the art in manufacturing silicon-integrated circuits. Other conventional methods have formed orientation-controlled platinum by depositing platinum on a glass substrate not on a silicon wafer, or by using a specially designed sputtering equipment which has an "auxiliary electrode" in order to deposit platinum film on silicon substrates. However, it has been reported that orientation-controlled platinum films deposited on glassy substrates have high resistivity (18 to 30 .mu..OMEGA.-cm) since oxygen, which was introduced during the deposition thereof, has remained within the platinum films even after annealing for 10 days. Therefore, it has been thought to be difficult and impractical to apply this process to real manufacturing practices, due to the very long annealing time. Furthermore, the platinum films formed on a silicon wafer by the conventional methods using sputtering are not dense enough and may have a number of pinholes, pores or hillocks, which may result in device performance problems.
The aforementioned drawbacks have been resolved by the inventions disclosed in Korean Patent Application No. 94-31618 filed on Nov. 26, 1994 and No. 95-40450 filed on Nov. 8, 1995 (corresponding U.S. application Ser. No. 08/562,371, filed Nov. 22, 1995) and No. 96-7663 filed on Mar. 21, 1996 (corresponding U.S. application Ser. No. 08/688,521, filed Jul. 30, 1996) by the present applicants' technology of depositing a platinum film on a silicon wafer under an atmosphere containing oxygen having preferred (200) orientation. According to these inventions, platinum thin films deposited on a silicon wafer with an insulating oxide layer have good adhesion strength and preferred (200) orientation.
It is seen from the above that alternative and improved methods for forming preferred orientation-controlled platinum films onto silicon substrates as well as other substrates are needed. It is desirable that such methods be compatible with silicon-integrated circuit technology in some applications. It is also desirable that such preferred orientation-controlled platinum films having minimized pinholes, pores or hillocks in order to provide improved device performance.